Internal combustion engines require a source of combustion air. A typical source for combustion air is air drawn from outside of the vehicle, which commonly includes particulate contaminants. An air cleaner including an air filter element is normally provided in the air induction system to capture these particulate contaminants before combustion air is delivered to the vehicle engine.
Air filters include filter media having relatively small pores for air flow therethrough that operate to inhibit the passage of undesired particulate contaminants. Since the presence of a filter media in the intake air stream acts to restrict air flow, air flow through the filter element necessarily produces a pressure differential or pressure drop between the filter element inlet and outlet surfaces (i.e. across the filter media). This air flow induced pressure drop produces deflection forces in the filter media of the filter element. These deflection forces are aligned with the air flow direction and, (for example) in panel type air filters, the deflection forces are typically normal to plane defined by the filter element media. The deflection forces tend to distort, deflect or “crown” the filter element.
Air filter elements are often made of pleated filter paper media secured to a periphery support frame, such as a molded plastic or elastomeric frame. Pleating the filter paper media increases the available filter surface area, while the pleats additionally serve to reinforce the filter media of the filter element against deformation or deflection due to air flow induced forces. In normal operating conditions this is usually sufficient.
Operation of the engine and its associated induction air filter in an adverse climate can substantially increase deflection force loading on the media of the filter element. In cold climates the air filter can draw in snow and ice pellets. The drawn-in snow is blocked by the filter element, accumulates at the dirty side of the filter element and acts to further block air flow through the filter element thereby increasing the pressure drop across the filter element together with an increase in deflection forces acting upon the filter media. Similarly, some varieties of filter media, such as types of filter paper, are prone to absorbing water droplets from the intake air stream, for example if operated in rainy or dense fog conditions. Water wets the filter media, obstructs pores in the media and may act to further obstruct air flow through the media with the resultant further increase in pressure drop and resultant deflection forces.
As can be seen, there is a need for an improved air filter element that provides improved resistance to filter media deformation without unduly increasing filter element cost or complexity.